Pressure sensors including microelectromechanical systems (MEMS) and associated chip systems are known; for example, such pressure sensors are used in therapeutic implants in order to improve the heart function of a patient. Chip systems used for such purposes must on the one hand deliver sufficiently precise measurement results, and on the other hand must have very small dimensions so that they can be implanted without difficulty and do not limit the physiological activity of the organism, for example, when used for blood pressure measurements in the pulmonary artery.
A MEMS chip must generally be protected if it is to be used in a reactive medium, for example in blood. Such protection is often provided by embedding it in an incompressible and inert liquid, and hermetically sealing it in a housing with respect to the reactive medium. The liquid (for example oil) here serves as a pressure transfer medium so that the external pressure can be conducted via the housing (often via a thin membrane on the housing), through the liquid, and to the MEMS chip. Titanium, for example, is suitable as a housing material on account of its long-term stability and high biocompatibility.
In the patient's blood, temperature changes of a few degrees Celsius can usually occur, thus resulting in volume and pressure changes of the pressure transfer medium within the housing. The chip also experiences temperature changes during sterilization, for example by means of ethylene oxide, wherein temperature differences of approximately 30 degrees Celsius occur. Such temperature (and thus volume and pressure) increases can damage the housing's membrane or the MEMS chip where a conventional pressure sensor housing is provided. The housing usually has a low flexibility or elasticity due to the material properties of the housing and the relatively high thickness of the housing walls in comparison to the overall size of the housing, and thus the pressure transfer medium's volume changes lead to high pressure changes within the housing. As a result, the measured pressure values of the MEMS chip are distorted because the pressure values to be measured are superimposed with temperature-induced pressure fluctuations inside the housing.
U.S. Pat. No. 8,573,062 describes the use of a pressure transfer membrane for a MEMS chip sensor, with the membrane covering a window which is formed in the side wall of the housing of the sensor. U.S. Pat. No. 8,142,362 describes a pressure transfer membrane situated on the end face of the housing.
Previous solutions for reducing the temperature dependence of MEMS chip sensor systems cannot reduce the distortions in measured pressure values to negligible levels compared with the pressure values to be measured in the body. Further problems include relatively high manufacturing expense and the housings limited ability to withstand material stresses and forces arising from volume changes of the pressure transfer medium. Joints created in the housing during manufacturing can be torn open by tensile stresses when the internal volume of the housing expands.